1. Field of the Invention
The present invention disclosed in the present specification relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, instead of a bulk silicon wafer, integrated circuits using an SOI (silicon on insulator) substrate have been developed. By utilizing a feature of a thin single crystal silicon layer formed over an insulating layer, a semiconductor layer of a transistor formed in the integrated circuit can be electrically separated from each other completely. Further, since the fully depleted transistors can be formed, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
In addition, a method for forming an SOI substrate in which a single crystal silicon layer is bonded to a glass substrate is known (see, for example, Reference 1: Japanese Published Patent Application No. H11-097379). In Reference 1, a separation surface is mechanically polished to remove a defective layer which is formed through hydrogen ion implantation or a step of several to several tens of nanometers on the separation surface.
Further, Reference 2 (Japanese Published Patent Application No. H11-145438) discloses the following: a surface on the SOI layer side of a single crystal silicon wafer to which hydrogen ions are introduced is disposed in close contact with an insulating substrate at room temperature; heat treatment is performed at 100° C. to 300° C. to temporarily bond the single crystal silicon wafer and the insulating substrate together; a single crystal silicon layer is etched; heat treatment at 350° C. to 450° C. is performed on the single crystal silicon wafer and the insulating substrate to finally bond the single crystal silicon wafer and the insulating substrate together; heating at 500° C. or higher is performed to make separation occur with a hydrogen ion implantation layer used as a cleavage plane, so that the single crystal silicon layer is formed as an SOI layer.
On the other hand, as a method for performing heat treatment on a silicon thin film over a substrate, a laser annealing apparatus for processing a laser beam and a microwave by being combined has been known (see, for example, Reference 3: Japanese Published Patent Application No. 2001-223175). Reference 3 discloses a method in which, by irradiating silicon melted by a laser beam with a microwave, cooling time is prolonged more than the case where silicon is melted only by a laser beam to expand silicon crystallization depth.